The International Journal of Artificial Organs / Vol. 18/ no. 9, 1995/ pp. 544-547 Urea Kinetics Biochemical aspects and clinical perspectives of continuous urea monitoring in plasma ultrafiltrate Preliminary results of a multicenter study G. COLASANTI 1 , G. ARRIG0 1 , A. SANTOR0 2 , S. MANDOLF0 3 , C. TETTA 4 , R. BUCCi 1 , M. SPONGAN0 2 , E. IMBASCIA TP, V. RIZZA 5, D. CIANCIA VICCHIA 4 1 Department of Nephrology, Ospedale San Carlo, Milano 2 Department of Nephrology, Ospedale Malpighi, Bologna 3 Department of Nephrology, Ospedale Maggiore, Lodi 4 Department of Clinical Chemistry, Ospedale San Carlo, Milano 5 Bellco SpA, Mirandola (Mo) - Italy ABSTRACT: We tested a new biosensor for urea monitoring in the ultrafiltrate during PFD in a group of 5 hemodialyzed stable patients. The inspection of the UF-urea profile reflects the dynamical changes of the plasma urea concentration during diffusive dialysis and allows the fitting of the main mathematical models of urea kinetics. The biosensor efficiency was 98.4% on average (SD: 1.5%) at Uf fluxes varying from 45 to 55 ml/min (mean: 51 mttrnin; SD: 3.2) and at Uf-urea concentrations varying from 23 to 165 mg/dl. The mean difference between Ut- urea determined by the laboratory method and Uf-urea assayed by the biosensor was -1.07 mg/dl and the 95% confidence interval ranged from -2.01 to 0.13 mg/dl. The mean difference between laboratory plasma urea and Uf-urea from the biosensor was on average -1.9 mg/dl and the estimated limits of agreement with a confidence of 95% were -3.16 and 0.64 mg/dl. Comparison between kinetic models and experimental profiles of plasma urea decrease, evaluations of recirculation and post-dialytic rebound, the role of Kt/V on-line during dialysis were the preliminary clinical applications of this biosensor. (Int J Artif Organs 1995; 18: 544-7) KEY WORDS: Paired Filtration Dialysis, Urea modeling, Kt/V, On-line monitoring INTRODUCTION The search for a quantitative prescription and de- termination of dialysis adequacy has renewed interest in studies of mass balance and the kinetic modeling of urea, which can still be considered the best marker of body depuration in the uremic syndrome. Performing urea kinetic modeling calls for a consid- erable number of timed blood samples, leading to the necessity of developing iterative algorithms based only on two or three blood samples (1). In this paper we describe a new urea biosensor (Bellco, Mirandola, Italy) which allows continuous monitoring of the urea concentration (Uf-urea) in the ultrafiltrate fluid during Paired Filtration Dialysis (PFD). The biosensor consists of a urease-bounded cartridge, coupled with a transducer which gives the measurement of the biochemical reaction. The use of this device, 0391-3988/544-04 $02.00/0 together with computer data management and analysis facilities, offers the opportunity of actual urea kinetic modeling without any need for blood sampling. The aim of this study was to test the reliability and the efficiency of this urea biosensor during PFD in a number of chronic patients, in comparison with urea determinations made by current laboratory methods. Furthermore, we present some new perspectives on possible clinical applications arising from the analysis of biosensor-derived urea profiles. MATERIALS AND METHODS Reagents All reagents were of analytical grade. In vitro calibration tests in aqueous solutions were carried out with different urea concentrations dissolved in glycine isotonic saline, pH 7.2. © by Wichtig Editore, 1995